Amplifier



April 18, 1933.

K. FOSTHUMUS AMPLIFIER Filed Feb. is, 1951 II a a main INVENTOR KLASSPOST HUMUS ATTORN EY Patented Apr. 18, 1933 STATES PATENT OFFICE KLAASPOSTHUMUS, OF EINDHOVEN, NETHERLANDS, ASSIGNOR TO RADIO CORPORA- T1017OF AMERICA, A CORPORATION OF DELAWARE AMPLIFIER Application filedFebruary 18, 1931, Serial No. 516,573, and. in the Netherlands March 26,1930.

This invention relates to improvements in amplifiers, and especially toimprovements in means for rendering the amplification of an amplifierindependent of the frequency of the oscillations impressed upon theamplifier input. It has been shown that the input circuit of anamplifier can be coupled with part of the output impedance in suchmanner that for all frequencies the alternate potential set up betweenthe terminals of the output impedance is proportional to the voltageamplitudes of the incoming oscillations. In a circuit arrangement ofthis type the impedance occurring in the external circuit is onlyconsidered and not the plate-filament capacity. Especially in the caseof higher frequencies, however, this capacity may also have a veryannoying effect.

Now the present invention has for its object to provide means forneutralizing the unevenness of the amplification caused by thiscapacity. It is not possible to directly utilize part of this capacityfor back coupling. Therefore a capacity in series with a resistance isinserted in the output circuit in parallel to this internal tubecapacity, the input circuit being coupled with part of the firstmentioned capacity in combination with the back coupling above referredto.

The currents passing through both capacities have the same phase. Whencoupling the input circuit with part of the capacity interposed in theoutput circuit, the same effect may be obtained as if it were directlycoupled with the plate filament capacity. Since the total capacity isgreater than this inserted capacity, the part of the latter which has tobe coupled with the input circuit, will be greater than that of theremaining impedance in the output circuit.

The novel features which I believe to be characteristic of my inventionare set forth in particularity in the appended claims, the

invention itself, however, as to both its or- I ganization and method ofoperation will best be understood by reference to the followingdescription taken in connection with the drawing in which I haveindicated diagrammatically one circuit organization whereby my inventionmay be carried into efiect.

In the output circuit of the thermionic tube 1 an impedance 2 isinserted, which serves for coupling with the next tube 3, and in seriestherewith an ohmic resistance R, of which a part R is coupled to theinput circuit. A capacity C is connected in parallel to the internalcapacity of the tube denoted in dotted lines by C, the capacity alsobeing in series with the ohmic resistances R and R The resistances R andR may be adjustable. Due to the anode currents, voltage variations areset up at these ohmic resistances, said variations being returned inopposite phase to the grid of the tube by a transformer 3 having anamplification factor equal to unity. Instead of this transformer 3, anysuitable transmission element may be used; for example, a triode havingan amplification factor 1.

One terminal of impedance 2, which is connected to the negative side ofthe anode potential source E, is connected to the grid of tube 3 throughthe direct current blocking condenser 3". The cathode of tube 3 isconnected to the cathode side of transformer 3, the usual grid biasresistor 4 being connected between the grid and cathode of tube 3.

The following analysis results in the values to be given to R and R inorder to obtain a uniform amplification: Letting R denote in thiscircuit arrangement the internal resistance of the tube; Z the externalimpedance, the plate filament capacity being included; R, the part ofthe output impedance serving for coupling with the next tube, R can thusbe considered equal to the value Z would have if C=C =O; s the mutualconductance; g the amplification factor; 12,, the anode alternatingvoltage; z', the anode al-' ternating current; e the grid voltage set upby signals; and 42 the grid voltage set up by back coupling, then:

1 1 i I 12,,( S (1),, 22 (I) Z is constituted by the impedance R whichfor example, may be inductive, the capacities C and C and theresistances of R and R which may be neglected relatively to the valuesof R C and C. 1

V is the sum of the tensions set up by R, and C respectively in R and R+R It has been assumed that the resistance of the primary Winding of the1 to l transformer 3 is so great, that the currents passingtherethroughmay be neglected.

Hence the Equation (I) maybe written:

wherein the terms and 8 (e are independent of the frequency, whlle allother terms depend thereon.

Assuming therefore,

was), a

This condition is satisfied if J l S R 01 S n 1, and

Since SR 1,it follows therefrom that A uniform amplification throughoutthe whole frequency range may consequently be obtained, by giving E andsuch values that R R like G: O and SR =L Preferably C is given about thesame value as C.

While I have indicated and described one arrangement for carrying myinvention into effect, it will be apparent to one skilled in theart thatmy invention is by no me ans limited to the )articular organizationshown and described, ut that many modifications may be made withoutdeparting from the scope of my invention as set forth in the appendedclaims.

Vhat I claim is 1. In combination, in an amplifier, an electrondischarge tube provided with an input and output circuit, a succeedingtube, a coupling path between the output circuit of the first tube andthe input circuit of the second tube, said path including an impedancein series with a resistor, a second path in shunt with said impedanceand including a condenser in series with a second resistor, and meansfor transmitting the drop of potential across a predetermined. portionof tial across said second resistor and a presaid first resistor to theinput circuit of the first tube.

2. In combination, in an amplifier, an electron discharge tube providedwith an input and output circuit, a succeeding tube, a coupling pathbetween the output circuit of the first tube and the input circuit ofthe second the ratio of the magnitudes of said resistors being equal tothe ratio of the magnitudes of the condenser and the cathode to anodecapacity of the first tube.

3. In combination, in an amplifier, an electron discharge tube providedwith an input and output circuit, a succeeding tube, a couqr pling pathbetween the output circuit of the first tube and the input circuit ofthe second tube, said path including an impedance in series with aresistor, a second path in shunt with said impedance and including acondenser in series with a second resistor, means I)? for transmittingthe drop of potential across a predetermined portion of said firstresistor to the input circuit of the first tube, means for adjustablyconnecting the-condenser to the second resistor, means for adj ustably0011- All necting the second resistor to the first resistor, and saidtransmitting means consisting of a l to 1 transformen i I i. Incombination, in an amplifier, an elec tron discharge tube provided withan input li and output circuit, a succeeding tube, a coupling pathbetween the output circuit of the first tube and the input circuit ofthe second tube, said path including an impedance in series with aresistor, a second path inshunt with said impedance and including acondenser in series with a second resistor, and means for transmittingthe drop of potendetermined portion of said first resistor to t theinput circuit of the first tube. I

KLAAS POSTHUMUS.

